CHAPTER 12THE CARDIOVASCULAR

SYSTEM: THE HEART

PAGES 388 - 411

LOCATION & GENERAL FEATURES OF THE HEART

TWO CIRCUIT CIRCULATORY SYSTEM

DIVISIONS OF THE HEART

FOUR CHAMBERS Right Atrium

Receives blood from the systemic circuit

Left Atrium Receives blood from

the pulmonary circuit

FOUR CHAMBERS Right Ventricle

Ejects blood into the pulmonary circuit

Left Ventricle Ejects blood into the

systemic circuit

FOUR VALVES – ATRIOVENTRICULAR VALVES

Right Atrioventricular Valve (AV) Tricuspid Valve

Left Atrioventricular Valve (AV) Bicuspid Valve and

Mitral Valve

FOUR VALVES – SEMILUNAR VALVES Pulmonary valve

Guards entrance to the pulmonary trunk

Aortic Valve Guards entrance to

the aorta

FLOW OF BLOOD

MAJOR VEINS AND ARTERIES AROUND THE HEART

• Arteries carry blood AWAY from the heart

• Veins allow blood to VISIT the heart

MAJOR VEINS AND ARTERIES ON THE HEART

Coronary Circulation – Supplies blood to the muscle tissue of the heart

ARTERIES

Elastic artery: Large, resilient vessels. pulmonary trunk and aorta

Muscular artery: Medium-sized arteries. They distribute blood to skeletal muscles and internal organs. external carotid artery of the neck

Arteriole: Smallest of arteries. Lead into capillaries

VEINS

Large veins: Largest of the veins. Superior and Inferior Vena Cava

Medium-sized veins: Medium sized veins. Pulmonary veins

Venules: the smallest type of vein. Lead into cappilaries

CAPILLARIES

Exchange of molecules between blood and interstitial fluid.

FLOW OF BLOOD THROUGH HEART

TISSUES OF THE HEART

THE HEART WALL Pericardium

Outermost layer Serous membrane

Myocardium Middle layer Thick muscle layer

Endocardium Inner lining of pumping

chambers Continuous with endothelium

CARDIAC MUSCLE Depend on oxygen to obtain energy

Abundant in mitochondria In contact with several other cardiac muscles

Intercalated disks – interlocking membranes of adjacent cells Desmosomes Gap junctions

CONNECTIVE TISSUE Wrap around each cardiac muscle cell and

tie together adjacent cells.

Provide support for cardiac muscle fibers

Add strength and prevent overexpansion of the heart

Help the heart return to normal shape after contractions

CHORDAE TENDINEAE Cord-like tendons that connect the papillary

muscles to the tricuspid valve and mitral valve

Connected to Papillary Muscle. Cone shaped projections on the inner surface of

the ventricle Contraction of papillary

muscles tenses the chordae tendineae and prevents the backflow of blood into the right and left atrium.

WHY DO YOU THINK THE LEFT VENTRICLE HAS THE LARGEST AMOUNT OF MUSCLE??

ELECTRICAL ACTIVITY OF THE HEART

THE HEARTBEAT

The entire heart – atria and ventricles – contracts in a coordinated manner so that blood flows in the correct direction at the proper time.

Two Types of Cardiac Muscle Cells Involved Contractile cells – contractions that propel blood Specialized noncontractile muscle cells – control and

coordinate the activities of the contractile cells in the heart Part of the conducting system

THE CONDUCTING SYSTEM A network of specialized

cardiac muscle cells that initiates and distributes electrical impulses. Nodal Cells

Located at the sinoatrial and atrioventricular nodes

Responsible for establishing the rate of cardiac contraction.

Coupled to one another causing a coordinated contraction when an action potential is initiated.

Conducting Cells Include the Atrioventricular Bundle,

bundle branches, and purkinje fibers

Responsible for distributing the contraction

THE CONDUCTING SYSTEM CONT.

Pacemaker Cells – Depolarize rapidly, generating 70 – 80 action potentials per minute (bpm) Located in the sinoatrial node

Atriventricular (AV) Bundle – (the bundle of His) extend along the interventricular septum before dividing into left and right ventricles

Purkinje Fibers – Convey the impulses to the contractile cells of the ventricle muscles.

THE ELECTROCARDIOGRAM

A machine that records the electrical events occurring in the heart.

Each time the heart beats a wave of depolarization radiates through the atria, reaches the AV node, travels down the interventricular septum to the apex, turns, and spreads though the ventricular muscles towards the base of the heart.

THE CARDIAC CYCLE

THE CARDIAC CYCLE

The peiod between the start of one heartbeat and the start of the next is a single cardiac cycle.

Includes a period of contraction - systole The chambers contract squeezing blood into an

adjacent chamber or arterial trunk

Includes a period of relaxation – diastole When the chambers fill with blood and prepares

for the start of the next cardiac cycle.

HEART DYNAMICS Refers to movements and forces generated during

cardiac contractions. Each time the heart beats, two ventricles eject equal

amounts of blood

Stroke volume - is the amount ejected by a ventricle during a single beat Stroke volume varies beat to beat so physicians are

often more interested in cardiac output

Cardiac output - is the amount of blood pumped by each ventricle in 1 minute Provides indication of blood flow through peripheral

tissues; without adequate blood flow, homeostasis cannot be maintained

FACTORS CONTROLLING CARDIAC OUTPUT

The major factors that regulate cardiac output often affect both heart rate and stroke volume

Primary factors include: Blood volume reflexes Autonomic innervation hormones